1. Field of the Invention
This invention relates to an apparatus for optically detecting the displacement (amount of movement, amount of rotation, speed and acceleration) of an object, and specifically to an encoder, a speed sensor, an acceleration sensor or the like.
2. Related Background Art
Optical displacement sensors for directing light to an object and detecting the displacement of the object highly accurately, for example, optical type encoders, laser Doppler velocity meters, laser interferometers, etc. are widely utilized in the fields of NC machine tools, OA instruments, robots, precision manufacturing apparatuses, etc.
One of these displacement sensors is a high resolving power sensor using interference light having the displacement information of an object to be inspected.
At present, as the displacement sensor using said interference light, there is required one which can stably obtain displacement detection signals of two or more differing phases.